Teensy 4.0 to 3.2 adapter card


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Are there any small boards that exist to adapt a teensy 4.0 into a 3.2 pinout?

I know the differences with various pin changes and voltage levels. And I see several projects (ornament and crimes eurorack modular, euroshield by 1010music, etc) that were designed for the teensy 3 series, but could really be brought back to life with a teensy 4.0, considering the limited availability of the 3.x.

Before I dove into making a board, I thought I'd seek info from the community. Forum and internet searches are both empty and flooded with noisy results.

It really depends on what is used in the Teensy 3.2. As Paul said, the Teensy 4.0 is as close as he could get to being 3.2 compatible. If you only use the basic ports (first serial port, first I2C bus, first SPI bus, using A0..A9 for analog input) it may already work.

Things in the 3.2 that are not available in 4.0:

  • Digital pins that can accept 3.4 to 5 volts of input without frying the Teensy;
  • Pins that support touch reading;
  • Analog input pins A10, A11 on the inside row;
  • Analog ground pin between VIN and 3.3v (that pin is now normal ground, and a special analog ground is not provided);
  • AREF pin on the inside row (you can use 3.3v as the analog reference);
  • Analog input/output pin A14 (typically A14 is used to connect to an amplifier and a speaker for low quality sound -- this isn't available in the 4.0, but there are ways to do sound);
  • Underneath pads on the Teensy 3.2 (Teensy has a different set of underneath pads, but not compatible with the Teensy 3.2 layout); (and)
  • Special SPI CS/DC pins that some display drivers can optimize for faster displays (typically it will just work but you won't get the optimization that the Teensy 3.x had for those displays).

Things that exist but use different pinouts:

  • Serial2 and Serial3;
  • Audio support (need different shield);
  • Alternative SPI ports (typically used because the I2S audio on the Teensy 3.x used 2 of the SPI pins);
  • Alternative I2C ports on pins 17 & 16 (pins 17 & 16 are a second I2C bus on Teensy 4.0); (and)
  • Flow control support for Serial devices (it exists, but it uses different pins IIRC).
Thanks guys. These are mostly audio applications, and are previously existing commercial products. So design or redesign of the original products is more difficult or not possible. Source code seems more readily available (since that is what the hardware offers...develop your own effects/app). So I thought I'd just shimmy in the 4.0 in place of a 3.2 that is called for.

My idea being a small board with both foot prints, and the connections between them (or minimal components) needed for the translation. Then I'd add .1" headers for the 3.2 footprint, and mount the 4.0 to the board. IN essence a surfboard to translate the pinout.
So I thought I'd just shimmy in the 4.0 in place of a 3.2 that is called for.

It's a nice idea, and you're certainly not the only person to have hoped for this. But the reality of the underlying technology an adaptor board that provides 100% compatibility just isn't feasible. The processors on Teensy 3.x and 4.x simply differ in ways that no adaptor board can resolve.

The very best adaptor which could be made is already "baked in" to the Teensy 4.0 design.